Various Stages Of Metamorphosis Research Articles

Art, science, and technology of outdoor advertising in Ghana

Outdoor advertising has been the most popular form of visual advertising from ancient times till now. The craft has gone through various stages of metamorphosis from crude painted signs to the pres...

The politics of minoritarian becomings: a Deleuzian approach to Macbeth and Othello

This paper intends to bring together the plots of Shakespeare’s Othello and Macbeth through examining their leading Shakespearean figures under the light of Deleuzian thought. A Close study of the two texts reveals these two Shakespearean plays as sites for excessive barbarism recited in form of verbal achievements in which a series of minoritarian becomings/mutations take place to consequently dislocate and disturb the majoritarian tradition by depicting identities that are open to change and mutation, and to show the majoritarian system, along with its Oedipalizing forces, as unorganized and faulty. Findings indicate that in the two plays, the identities of the two leading characters of Macbeth and Othello undergo various stages of metamorphosis through which both try to form their temporary lines of flight and have their specific mode of liberation and deterritorialization from majoritarian forces that are dominant in either of the two hegemonic domains to which they belong. Also discussed is Shakespeare’s writing which, in this sense, qualifies as minor literature in that it depicts such a series of transformations and becomings against the long-held belief of stable identity, and lets the readers become one with the process of reading and hence challenge the identities that are forced upon them.

Tadpole eyes swivel and cross during metamorphosis

The changes that most animals experience during the transition from juvenile to adulthood can be disruptive and inconvenient, but pale into insignificance in comparison with the drastic metamorphosis that amphibians undergo. Denis Combes and colleagues from the University of Bordeaux, France, and the Ludwig-Maximilians-University Munich, Germany, describe how metamorphosing tadpoles have to adapt from a wriggling swimming style to a forward thrusting motion with each kick of their newly emerged hind legs. However, this transition is also accompanied by a change in the tadpoles’ vision. Wriggling tadpoles swivel their eyes in the opposite direction from their weaving bodies to hold their view of the world steady, while kicking froglets cross their eyes in time with each kick to maintain their view of objects as they appear to loom when the tiny amphibians surge forward. The nerve signals that drive these eye movements are coordinated by the signals that control the respective swimming movement, so Combes and his colleagues Géraldine von Uckermann, François Lambert, Hans Straka and John Simmers wondered how Xenopus tadpoles maintain gaze control during the critical transition period from one swimming style to the other.The team recorded the nerve signals controlling the eye movements and swimming muscles of tadpoles, in addition to filming the motion of the tadpoles’ eyes, at various stages of metamorphosis. After analysis of the nerve signal patterns, they discovered that the eye control signals gradually shift from regulating the eyes as they swivel to coordinating both swivelling and looming eye movement patterns simultaneously, until the eye swivel pattern dwindles away and the tadpoles switch exclusively to converging the eyes as they kick-swim at the end of the metamorphosis. The team also realised that the nerve signal pattern that coordinates the eye movements with the swimming action switches gradually from the signals that control the wriggling swim to those driving the adult-style leg kick, allowing the tadpole to transition seamlessly from one lifestyle to the other.

Assessment of Egg and Larval Quality during Hatchery Production of the Temperate Sea Cucumber, Australostichopus mollis (Levin)

Abstract A greater understanding of the causes of variation in egg and larval quality during larval rearing of sea cucumbers will assist in the development of methods to further improve production in hatcheries. For Australostichopus mollis the techniques and methods used in other hatcheries during fertilization resulted in polyspermy occurring in 10–60% of spawned eggs. Despite this, hatch rates were usually greater than 90%. By Day 18 when fed the diatom Chaetoceros muelleri at 2000 cells/mL/day, survival in cultures varied between 35 ± 26% and 57 ± 25%. Of remaining larvae, 10–12% remained in the water column for long periods and did not complete metamorphosis. Furthermore, observation of development in relation to growth and feeding rather than gut content was a better indicator of larval competence. Larvae that were between 700 and 1000 ± 50 μm in length had between four and eight hyaline spheres in the folds of the ciliated band and were in various stages of metamorphosis and settlement. Assessment and comparison of current and previous methods enabled a greater understanding of sources of variation in egg and larval quality, impacts on the production cycle, and suggested improvements.

The role of androgen in the development of sexual differences in pituitary responsiveness to gonadotropin releasing hormone (GnRH) agonist in the bullfrog, Rana catesbeiana

Sexual differences in pituitary responsiveness to acute injection of gonadotropin-releasing hormone (GnRH) agonist, as measured by increments in plasma FSH and LH, were examined throughout development in the bullfrog, Rana catesbeiana. Untreated tadpoles, in various stages of metamorphosis, were unresponsive to GnRH agonist. Postmetamorphic males showed a progressive increase in the magnitude of pituitary response with age, whereas females remained relatively insensitive until after sexual maturation; males were always more responsive than females. Chronic (1–2.5 week) Silastic implants containing 5α-dihydrotestosterone (DHT) significantly augmented the pituitary response (for both gonadotropins) in intact postmetamorphic females at all ages; a similar, though less pronounced, action of testosterone in subadult females may have been due to its conversion to DHT. (Silastic implants of comparable size always produced higher circulating levels of DHT in females than in males as was observed in previous studies with gonadectomized frogs.) DHT enhanced the responsiveness of intact tadpoles (sexes undetermined); only the treated tadpoles responded to the GnRH agonist. Supplemental DHT did not enhance pituitary response in intact males; in fact, it attentuated the response in FSH. GnRH responsiveness paralleled changes in pituitary gonadotropin content; pituitary content of FSH and LH was higher in males than females; it showed a marked increase with age from tadpole to adult; and it was increased by DHT treatment. The potentiating effect of DHT on GnRH responsiveness and the significantly higher levels of DHT observed in males of all ages suggest that the nonaromatizable androgen DHT may be responsible for the early establishment and maintenance of sexual dimorphism in pituitary GnRH responsiveness in the bullfrog.

TRH, GH-RIH, and LH-RH in metamorphosing Xenopus laevis

Immunoreactive thyrotrophin-releasing hormone (iTRH), growth hormone release-inhibiting hormone (iGH-RIH), and luteinizing hormone-releasing hormone (iLH-RH) were measured in spontaneously developing Xenopus laevis tadpoles at various stages of metamorphosis. All three peptides were detected in animals at all stages of metamorphosis. Brain iTRH concentration increased markedly during prometamorphosis and metamorphic climax; skin iTRH concentration was low during prometamorphosis and increased at metamorphic climax. Brain iGH-RIH concentration increased to a maximum at prometamorphosis, then declined during climax; gastrointestinal tract iGH-RIH concentration increased progressively as metamorphosis proceeded; skin iGH-RIH concentration was low throughout metamorphosis. Brain iLH-RH concentration increased progressively during metamorphosis. The widespread tissue distribution of these hypophysiotrophic peptides suggests they might have endocrine and paracrine functions in amphibians. The rise in brain iTRH concentration during early prometamorphosis suggests that hypothalamic secretion of TRH might be the initiating event in thyroid hormone production and metamorphosis.

Plasma T 4 and T 3 levels in Ambystoma tigrinum at various stages of metamorphosis

Circulating T 4 and T 3 levels were measured in Ambystoma tigrinum at various stages of development with sensitive and reliable radioimmunoassays developed in this laboratory. The minimum detectable level with these procedures was estimated to be 50 ng/100 ml for T 4 and 5 ng/100 ml for T 3. Significant levels of circulating thyroid hormone were observed only during the period of metamorphosis and for several days postmetamorphosis. Plasma T 3 was more consistently elevated than plasma T 4. In larval and adult animals plasma levels of T 4 and T 3 were essentially undetectable. These results resemble those previously reported from this laboratory for Rana catesbeiana. The present findings provide evidence that in urodeles, as in anurans, elevation of circulating thyroid hormone levels is required for normal metamorphosis.

Plasma Thyroxine and Triiodothyronine Levels in Spontaneously Metamorphosing Rana catesbeiana Tadpoles and in Adult Anuran Amphibia*

We have developed sensitive and reliable radioimmunoassays for T4 and T3 in amphibian plasma and have used these procedures to measure plasma T4 and T3 levels in spontaneously developing Rana catesbeiana tadpoles at various stages of metamorphosis. During premetamorphosis circulating levels of both T4 and T3 were below the limits of detection of the RIA procedures (T4 less than 50 ng/100 ml, T3 less than 5 ng/100 ml). A gradual rise in plasma T3 and T4 became apparent during prometamorphosis, and at the onset of metamorphic climax the levels of both T4 and T3 increased sharply. Peak levels for both hormones were observed in the middle of metamorphic climax (stage XXIII). The circulating T3 level reached a mean peak of 78 ng/100 mg, at least 15 times greater than the level during premetamorphosis. The peak T4 level was 0.5 microgram/100 ml, about a 10-fold increase over the premetamorphosis level. The surge in thyroid hormone secretion lasted only for several days, and during the latter half of metamorphic climax there was a fairly rapid decrease in plasma T4 and T3. By 2 days post-climax the levels had declined to about 20% of their peak values. Free T4 and T3 levels in plasma followed the same general pattern as the total hormone levels during the various stages of tadpole development. In adult R. catesbeiana, plasma T4 and T3 levels were surprisingly low. Similarly low values were observed in Bufo marinus and in Rana pipiens. The very low levels of circulating T4 and T3 both in premetamorphosis tadpoles and in adults suggest that thyroid hormones in anuran Amphibia may be of importance only during the period of metamorphosis.

Changes in the tail of Ambystoma maculatum at different stages of metamorphosis: observations on tissue remodeling and its relationship to hydrolytic enzymes.

A system for staging A. maculatum during growth and metamorphosis was devised, based on several parameters of body size; body length, tail length and tail width. Animals at various stages of metamorphosis were employed to study the relationship between specific biochemical and histological changes that occur in the tail of this urodele during metamorphosis. The specific and total activity of two hydrolytic enzymes, acid phosphatase and beta-N-acetyl-glucosaminidase, were measured in tail tissues at progressive stages of development. The activities of these enzymes increased in both the fins and muscular portion of the tail during metamorphosis. These activities can be correlated with resorption of the tail fins and the remodeling of tissues in the muscular portion of the tail.

Effects of some insect development inhibitors on mosquito larvae

AbstractThe compounds tested were isopropyl (±)‐(E,E)‐11 ‐methoxy‐3,7,11‐trimethyl‐dodeca‐2,4‐dienoate (ZR 515) and 6,7‐epoxy‐3‐ethyl‐7‐methylnonyl 4‐ethylphenyl ether (R 20458) (two juvenile hormone mimics); 2,6‐di‐tert‐butyl‐4‐(αα‐dimethyl‐benzyl)phenol (MON 0585) (which inhibits melanisation during pupation); diflubenzuron and 1‐(4‐chlorophenyl)‐3‐(2,6‐dichlorobenzoyl)urea (PH 60:38) (which affect chitinisation during moulting); and (E)‐oct‐2‐enoic acid and (E)‐non‐2‐enoic acid (all of which are claimed to have “teratogenic” effects on insects). The relative potencies of these chemicals were assessed on eggs, larvae and pupae of several mosquito species. Their characteristic delayed harmful effects are described and related to various stages of metamorphosis.

An in vitro quantitative analysis of the response of tadpole tissue to thyroxine.

AbstractDorsal tail fins of tadpoles, (Rana pipiens) at various stages of metamorphosis, were cut into pieces or discs and then cultured either in Hanks balanced salt solution or Hanks containing L‐thyroxine (T4). Six concentrations of T4 were tested: 3, 9, 27, 81, 250, and 750 parts per billion (ppb). In addition, early prometamorphic discs were cultured in medium containing 3 ppb of T4 for different periods of time: 1, 3, 5, and 7 days and then placed into control medium for the remainder of the experimental period. Controls for this experiment were maintained continuously in either 3 ppb of T4 or in control medium. To test the specificity of response to T4 early prometamorphic discs were cultured in medium containing KI, DL‐thyronine or DL‐diiodothyronine. Discs respond to treatment with thyroxine by shrinkage. The degree of shrinkage was determined quantitatively by measurement of area.The results show that a direct quantitative relationship exists between concentration of thyroxine and resorption. Resorption is dependent upon the continuous presence of T4. It was also demonstrated that tail discs change in their sensitivity to thyroxine at progressive stages of metamorphosis. It is proposed that the increased sensitivity of tail tissues to T4 during metamorphosis results from their previous exposure to a low but rising level of thyroid hormone that increases sharply in the donor tissues one to two days before the emergence of the forelegs. Finally, it was demonstrated that these results represent the specific action of thyroid hormone.

The effects of neurohypophysial hormones on water and sodium balance in larval and adult bullfrogs ( Rana catesbeiana)

1. 1. The injection of arginine vasoticin into bullfrogs at various stages of metamorphosis influences their body weight. In young tadpoles (stages IV–X) handling stress causes a pronounced loss of weight. This can be reduced or abolished by injecting AVT. Older tadpoles and adult elicit a typical Brunn effect; the intensity increases with stage of metamorphosis and reaches a maximum in adults. 2. 2. Doses of oxytocin up to 110 mμmoles/kg fail to elicit a water-balance response in tadpoles younger than stages XXII. Stage XXII animals show a small responses (106 per cent of initial weight in 2 hr) when injected with 22 mμmoles/kg; lower doses were not tested. Animals in stages XXIII to XXV respond to doses of 2·2 mμmoles/kg (103 per cent in 2 hr) and 22 mμmoles/kg (115 per cent in 2 hr). 3. 3. Arginine vasotocin (3·3 mμmoles/kg) causes a net uptake of sodium in tadpoles and adults. In tadpoles this is mostly attributable to a reduction in the efflux which probably reflects a decrease in the renal loss of the ion. In adults the uptake results from a faster influx indicating an effect on the skin.

Quantitative investigation on the anterior pituitary-thyroid mechanism during frog metamorphosis.

IN A large number of previous investigations it has been definitely proved that in amphibians metamorphosis is dependent upon the normal functioning of the anterior pituitary-thyroid system (with regard to the extensive literature, see 1, 2). Little is known, however, regarding the variations in thyroid function during metamorphcsis and the corresponding changes in the thyrotropic activity of the anterior pituitary, and the statement commonly found in textbooks that thyroid activity increases during metamorphosis is based chiefly on morphological studies. Furthermore, the time relations between the supposed functional variations and between these and the various stages of metamorphosis have been subjected to little investigation. For this reason an attempt has been made to study the functional variations possibly occurring in the anterior pituitary-thyroid system during the various stages of metamorphosis using a quantitative method. The species used in this investigation was the South African clawed toad...

Immunological studies on insect metamorphosis. I. Qualitative and quantitative description of the blood antigens of the Cecropia silkworm.

1. The cell-free blood of the Cecropia silkworm produces a maximum of nine bands of antigen-antibody precipitate when reacted in antiserum-agar tests with antisera prepared by injecting Cecropia extracts into rabbits. The blood antigens producing these bands of precipitate have the properties of proteins in that they are non-dialyzable, labile at 75 degrees C., and salted out by 75 per cent saturated ammonium sulfate. One antigen was identified as a carotenoid protein. 2. Six bands of precipitate were selected for further study. Absorption tests revealed that the blood, at all stages of metamorphosis, is capable of precipitating the antibodies which produce five of these bands. This result indicates that five of the six antigens are present in the blood throughout metamorphosis. The sixth antigen is undetectable in blood from fourth instar larvae, appears in the blood late in the fifth instar, persists during the pupal stage, and disappears again during adult development. 3. When blood samples from various stages of metamorphosis were tested in antiserum-agar tubes, the rates of advance of the six bands of precipitate underwent systematic change in close correlation with the morphological stage of the silkworm's metamorphosis. These changes are interpreted in terms of concentration changes of the corresponding blood antigens. The validity of this interpretation was tested in several ways, with the conclusion that the interpretation was generally acceptable for the system under consideration. 4. All six antigens appear to increase in concentration during the last larval instar and to decrease in concentration during the period of adult development. However, each antigen has its own characteristic pattern of concentration change which differs from those of the other five. In order to explain this diversity, we conclude that the physiological mechanisms which regulate the synthesis and utilization of the blood antigens control each antigen on an individual basis.